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  <title>Document</title>
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<body>
  <script>
    // var obj = {
    //   uname: 'zs'
    // }

    // console.log(obj.uname)

    // number string boolean
    var str = 'qwer'

    // var test = new String('qwer')
    // test.length
    // test = null
    console.log( str.length  )

    // 字符串有一个不可变性, 所以 之后学习的字符串的方法，都是返回一个新的字符串，原来字符串不变

  </script>
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